1. Field of the Invention
The present invention relates to a light emitting device provided with a light emitting element and a means for supplying electric current to the light emitting element in each of a plurality of pixels.
2. Description of the Related Art
There will be described a structure of a pixel in a general light emitting device and a driving method thereof. A pixel shown in FIG. 5A has TFTs 80 and 81, a capacitor 82, and a light emitting element 83. It is not always necessary to provide the capacitor 82.
The TFT 81 has a gate connected to a gate line 85, one of a source and a drain connected to a source line 84, and the other connected to a gate of the TFT 81. The TFT 81 has a source connected to a power source line 86 and a drain connected to an anode of the light emitting element 83. The capacitor 82 is provided in order to keep voltage between the gate and the source of the TFT 81. To each of the power source line 86 and a cathode of the light emitting element 83, a predetermined voltage is given from a power source to have a potential difference each other.
It is noted that a connection in the present specification means an electrical connection, providing no specific notice is mentioned.
When the TFT 80 is turned on in accordance with an electric potential of the gate line 85, an electric potential of a video signal input to the source line 84 is given to the gate of the TFT 81. In accordance with the electric potential of the input video signal, a gate voltage (a potential difference between the gate and the source) of the TFT 81 is determined. Then, a drain current that flows in accordance with the gate voltage is supplied to the light emitting element 83 and the light emitting element 83 emits light in accordance with the supplied electric current.
A structure of a pixel in a general light emitting device, which is different from FIG. 5A, is shown in FIG. 5B. The pixel shown in FIG. 5B has TFTs 60, 61, and 67, a capacitor 62, and a light emitting element 63. It is not always necessary to provide the capacitor 62.
The TFT 60 has a gate connected to a first gate line 65, one of a source and a drain connected to a source line 64, and the other connected to a gate of the TFT 61. The TFT 67 has a gate connected to a second gate line 68, one of a source and a drain connected to a power source line 66, and the other connected to the gate of the TFT 61. The TFT 61 has a source connected to the power source line 66 and a drain connected to an anode of the light emitting element 63. The capacitor is provided in order to keep voltage between the gate and the source of the TFT 61. To each of the power source line 66 and a cathode of the light emitting element 63, a predetermined voltage is given from a power source to have a potential difference each other.
When the TFT 60 is turned on in accordance with an electric potential of the first gate line 65, an electric potential of a video signal input to the source line 64 is given to the gate of the TFT 61. In accordance with the electric potential of the input video signal, a gate voltage (a potential difference between the gate and the source) of the TFT 61 is determined. Then, a drain current that flows in accordance with the gate voltage is supplied to the light emitting element 63 and the light emitting element 63 emits light in accordance with the supplied electric current.
In addition, in the pixel shown in FIG. 5B, when the TFT 67 is turned on in accordance with an electric potential of the second gate line 68, an electric potential of the power source line 66 is given to the gate of the TFT 61, and therefore the TFT 61 is turned off and the light emitting element 63 is forced to finish emitting light.